Those who grow up in an atheist household are least likely to maintain their beliefs about religion as adults, according to a study by Georgetown University's Center for Applied Research in the Apostolate (CARA).

Only about 30 percent of those who grow up in an atheist household remain atheists as adults. This "retention rate" was the lowest among the 20 separate categories in the study.

There were 1,387 atheists (weighted) in the survey. Four-hundred thirty-two weighted respondents said they were raised atheist. Of those, 131 self-identified as atheist.

"What these findings reflect is that in the U.S. atheists are for the most part 'made' as adults after being raised in another faith. It appears to be much more challenging to raise one's child as an atheist and have them maintain this identity in their life," Dr. Mark Gray wrote at CARA's blog.

Gray also noted that, "of those raised as atheists, 30% are now affiliated with a Protestant denomination, 10% are Catholic, 2% are Jewish, 1% are Mormon, and 1% are Pagan."

Jehovah's Witness, congregationalist and holiness churches had the next lowest retention rates at 37 percent, 37 percent and 32 percent, respectively. Thirty-eight percent of those who grew up with no particular religious faith or belief system remained that way.

Baptists had the highest retention rate of the Protestant Christian categories at 60 percent, followed by Lutheran (59 percent) and Pentecostal (50 percent).

The study used the Pew Forum on Religion and Public Life's 2008 U.S. Religious Landscape Survey. Gray noted that Pew's original report did not include some of the retention rates. Pew provided CARA with the original data sets for the study.